Global Namespace

The Sun Cluster software mechanism that enables global devices is the global namespace. The global namespace includes the /dev/global/ hierarchy as well as the volume manager namespaces. The global namespace
reflects both multihost disks and local disks (and any other cluster device, such
as CD-ROMs and tapes), and provides multiple failover paths to the multihost disks.
Each node that is physically connected to multihost disks provides a path to the storage
for any node in the cluster.

Normally, for Solaris Volume Manager, the volume manager namespaces are
located in the /dev/md/diskset/dsk (and rdsk) directories. For Veritas VxVM, the volume manager namespaces are located
in the /dev/vx/dsk/disk-group and /dev/vx/rdsk/disk-group directories. These namespaces
consist of directories for each Solaris Volume Manager disk set and each VxVM disk
group imported throughout the cluster, respectively. Each of these directories contains
a device node for each metadevice or volume in that disk set or disk group.

In the Sun Cluster system,
each device node in the local volume manager namespace is replaced by a symbolic link
to a device node in the /global/.devices/node@nodeID file system where nodeID is an integer that
represents the nodes in the cluster. Sun Cluster software continues to present the
volume manager devices, as symbolic links, in their standard locations as well. Both
the global namespace and standard volume manager namespace are available from any
cluster node.

The advantages of the global namespace include the following:

Each node remains fairly independent, with little change in the device
administration model.

Devices can be selectively made global.

Third-party link generators continue to work.

Given a local device name, an easy mapping is provided to obtain its
global name.

Local and Global Namespaces Example

The following table shows the mappings between the local and global namespaces
for a multihost disk, c0t0d0s0.

Table 3–2 Local and
Global Namespace Mappings

Component or Path

Local Node Namespace

Global Namespace

Solaris logical name

/dev/dsk/c0t0d0s0

/global/.devices/node@nodeID/dev/dsk/c0t0d0s0

DID name

/dev/did/dsk/d0s0

/global/.devices/node@nodeID/dev/did/dsk/d0s0

Solaris Volume Manager

/dev/md/diskset/dsk/d0

/global/.devices/node@nodeID/dev/md/diskset/dsk/d0

SPARC: VERITAS Volume Manager

/dev/vx/dsk/disk-group/v0

/global/.devices/node@nodeID/dev/vx/dsk/disk-group/v0

The global namespace is automatically generated on installation and updated
with every reconfiguration reboot. You can also generate the global namespace by running
the scgdevs(1M) command.